It isn’t pretty and I have a lot of filing to do. I chain drilled enough that I could line up my dremel tool and finish up the hole. Amazing how hot the metal gets with a grinding wheel.
(Edit) forgot to add the blasted photo!
@va3db I work a lot of steel on belt sanders and yes it gets really hot really quickly! I have to have a dunk tank of water near my sanders, especially for metal where I don't want to destroy the temper or if I'm holding onto it by hand.
@croyle Yep yep! A belt sander would have been overkill for this. Sometimes I wish I had a mill for occasions like this!
@va3db A mill would be very useful, but they are a lot!... Have you considered one of those mini belt sander tools to smooth out that window? I have one but it's a cheap Harbor Freight model and it kind of sucks. :) But I love the idea. https://www.harborfreight.com/power-tools/sanders/belt-palm-sanders/belt/53-amp-12-in-x-18-in-bandfile-belt-sander-58155.html
@croyle Honestly it's pretty good now but a power tool would save a lot of filing!
@va3db Filing is cheap and versatile, but sometimes the time and effort that a power tool saves is better for your sanity! 
@croyle Aluminium is not a big problem for me as I can use a hand nibbler etc. and the filing isn't as painful. *sigh*